Two types of late-Ottoman public fountains: a ‘çeşme’ (on the right) and a ‘sebil’ (in the center of the picture).

Neither of the two still operating, they have been replaced by a modern box-shaped water disperser.

A çeşme (a kind of fountain) is a piece of architecture which supplies drinking water. They were connected to springs or aqueducts. Until the late 19th century most ‘çeşme’ operated by gravity, and needed a source of water higher than the fountain, such as a reservoir or aqueduct, to make the water flow.

A sebil is a kiosk-shaped public fountain, with grilled office-windows where attendants handed fresh water over to the public. Generally a sebil had a cellar, where large blocks of ice were brought in during winter. So, in summer, the drinking water could be cooled before distributing it.

Correspondent: J.M.Criel, Antwerpen.
Sources: (amongst others) ‘Guides Bleus: Turquie’ – Edition 198 & Wikipedia.

This particular one is part of the New Mosque complex according to Strolling through Istanbul. That book also explains that "sebil" literally is "way" or "path: "to construct a sebil was to build a path for oneself to paradise."